1. Field of the Invention
The invention relates to the field of wireless communications in which channel estimation and transmit beam forming occurs in a reconfigurable antenna array.
2. Description of the Prior Art
Many space-time transmission schemes have been proposed recently to exploit the high channel capacity from the MIMO communication systems. However, algorithms for a large antenna array (LAA) remain an open research problem. The standard channel estimation and space-time modulation schemes are not practical for LAAs due to high implementation complexity.
Channel estimation for MIMO wireless channels is well known as disclosed in D. Samardzija and N. Mandayam, “Pilot-assisted estimation of mimo fading channel response and achievable data rates,” IEEE Trans. Signal Processing, vol. 51, no. 11, pp 2882-2890, November, 2003. Further, transmit beam forming for MIMO wireless channels is described in Hottinen, O. Tirkkonen, and R. Wichman, Multi-antenna transceiver techniques for 3G and beyond, New York: Wiley, 2003. The inventors have also published the general idea of adapting the communication system to reconfigurable antennas as disclosed in B. A. Cetiner, H. Jafarkhani, J.-Y. Qian, H. J. Yoo, A. Grau, and F. De Flaviis, “Multifunctional Reconfigurable MEMS Integrated Antennas for Adaptive MIMO Systems,” IEEE Communications Magazine, December 2004.
Multiple-input multiple-output (MIMO) systems offer much larger channel capacity over traditional single-input single-output (SISO) systems. Usually, it is easy to mount multiple antennas at the base station instead of the mobile station since there are less space and power restriction. Thus, the embodiment of a multiple-input single-output system (MISO) is of special interest for high-rate downlink wireless communications.
Recently, many open loop and close loop algorithms have been developed for MISO systems. The open loop algorithms are based on space-time coding (STC) and no channel state information (CSI) is required at the transmitter. The close loop algorithms are normally referred to as transmit beamforming and they require channel state information at the base station. Usually, the channel state information can be sent back from the mobile station to the base station through a feedback channel. In the traditional MISO system, the channel capacity increases with the number of transmit antennas. However, each transmit antenna requires a dedicated RF chain which consists of analog front end, mixer, and power amplifier. As the number of transmit antennas increases, so do the cost and the power consumption of the transmitting unit at the base station. Moreover, for the purpose of coherent detection, the receiver needs to keep track of the multi-path fading channels between each transmit antenna and the receive antenna. The continuous channel estimation will consume a significant amount of power and processing resource on the mobile station. Since the portable mobile station has a strict power and cost concern, the real time channel estimation at the mobile station becomes a prohibitive task when the number of transmit antennas is large.
In addition, to implement transmit beamforming algorithms for a large number of transmit antennas, the mobile station needs to manage a large amount of channel state information feedback, which also increases the mobile station complexity.
Therefore what is needed is some type of system or method of communication which employs a low-cost low-complexity transmitter architecture that enjoys superior performance as well as simple implementation.